1. Field of the Invention
This invention relates to a horizontal type vulcanizer for continuously producing an elongated member such as a tube, hose, rod, electrically insulated wire and cable, and profile, made of natural or synthetic polymer such as rubbers and plastic materials. The elongated member is continuously passed through a liquid heat medium under pressure subjecting it to heat and vulcanization.
2. Description of the Prior Art
There is a significant disadvantage in conventional devices for continuously extruding and vulcanizing the material to produce elongated members in that the elongated member is deformed, if bent greatly or changed its travelling direction, during its incomplete vulcanization state. Therefore, a requirement exists to provide a horizontal type continuous vulcanizer in which the liquid heat medium is filled and wherein the elongated member in unvulcanized state just extruded from an extruder is substantially linearly passed through the liquid heat medium under pressure until the vulcanization is completed. In this case, a minute bend of the elongated member due to its weight or buoyancy is negligible.
In order to meet this demand, U.S. Pat. No. 4,029,450 discloses a horizontal type vulcanizer in which liquid heat medium (bath liquid) flowing down from the inlet and the outlet of the horizontal bath for passing the elongated member therethrough is recirculated into the bath by means of a pump. However, during operation it is rather difficult to recirculate under pressurized condition such liquid maintained at a high temperature, suitable for vulcanization of the elongated member, of about 200.degree. C. That is, a pump is required which sustains high temperature and high pressure. Furthermore, the recirculation system is required to have thermal resistance for a long duration, so that the system is complicated and costly.
In case of the employment of a bath liquid having a high melting point of about 100.degree. C. or more, such as eutectic mixed salt consisting of NaNO.sub.3, NaNO.sub.2 and KNO.sub.3, the temperature of the liquid in the recirculation system should be monitored during operation. If a low temperature region below the melting point of the liquid is generated in the portion of the recirculation system, the salt mixture is solidified thereat to thus block the liquid recirculation. Once the liquid recirculation is blocked, the vulcanizer is exposed to danger of explosion caused by the possible direct contact of cooling water with the bath liquid of high temperature which may flow into a cooling system. In the above-mentioned U.S. Patent, a vulcanizing tube having U-shaped in cross-section is also shown. According to this U-shaped tube, no problem may be arisen in terms of flowing down of the bath liquid above mentioned, and thus there is no necessity of recirculating the bath liquid. However, it would be rather difficult to pass the elongated member through the U-shaped vulcanizing tube under tension control, especially in the case where the elongated member has a specific gravity lower than that of the bath liquid, and therefore floats in the bath liquid.